1. Field of the Invention
The present invention relates to a flat-panel display unit, such as a plasma display or a liquid-crystal display.
2. Description of the Related Art
Inside of the frame body of electronic equipment, a signal-transmission cable is used to transmit a signal between circuit substrates. In recent years, a thin sheet-type flexible cable (which is generally called an FFC (or flexible flat cable) or an FPC (or flexible printed circuit)) has become more popular as electronic equipment becomes smaller and denser. In such a flexible cable, its connecter is smaller than that of any other conventional flat cable. Thereby, the area necessary for mounting a cable on a circuit substrate becomes smaller. Additionally, the flexible cable is thinner and more flexible resulting in a greater degree of freedom. For reasoning in addition to those discussed above, the thin sheet-type flexible cable has been used.
The problem of electromagnetic wave noise apparent as a signal is transmitted faster (i.e. with a higher frequency). Electro-magnetic wave noise is radiated from a cable transmitting a signal between circuit substrates inside of electronic equipment. In order to restrain the emission of such an electro-magnetic wave noise, for example, Japanese Patent Laid-Open No. 2002-117726 specification discloses a case where a thin sheet-type flexible cable is subjected to shielding. FIG. 8 schematically shows the configuration of a shielded flexible cable 108.
In this flexible cable 108, a sheet-shaped shield conductor 102 and a sheet-shaped insulator 101 are formed in layers. The entire stratified body is covered with an insulating coat 107. Inside of the insulator 101, several conductive wires are provided in parallel. These conductive wires are a high-speed signal line 103 such as a clock signal line, a low-speed signal line 106 such as a ground line 104, a shield ground line (or a shield drain line) 105, a control signal line, and the like. The shield ground line 105 is used to connect the shield conductor 102 to the ground of a circuit substrate to which the flexible cable is connected. The shield ground line is connected to the shield conductor 102. The ground line 104 is not connected to the shield conductor 102 and is separate. In this flexible cable 108, the high-speed signal line 103 and the shield ground line 105 are adjacently disposed for the purpose of shielding. In addition to those lines, a power-source line and other signal lines are provided in the flexible cable 108. However, in the figure, they are omitted, and thus, only conductive, wires which are related to the following conventional disadvantages, are shown.
In the above described flexible cable 108 which is subjected to shielding, the shield conductor 102 and the shield ground line 105 contribute to reducing electro-magnetic wave noise. However, because the cable requires a multi-layer structure, it becomes an extremely expensive flexible cable. Additionally, as shown in FIG. 4A, if a flexible cable 11 connects substrates, some play is given. Therefore, as shown in FIG. 4A, the flexible cable 11 is disposed so as to bulge out.
However, if a flexible cable is used, for example, to connect substrates which are attached to an aluminum chassis 2 inside of a plasma display, then the aluminum chassis 2 is connected to a drive-system ground, a signal-system ground and a frame body. This generates a stray capacitance between the flexible cable 11 and the aluminum chassis 2. Therefore, when the flexible cable 11 is connected with such play, some dispersion can be produced in the bulge shown in FIG. 4A, thus dispersing the stray capacitance. In addition, a flexible cable is flexible and its shape is easily changed. Hence, as the shape is changed, the stray capacitance is also changed. In this case, the more largely the flexible cable 11 bulges out from the aluminum chassis 2, the lower the stray capacitance, resulting in the higher-harmonic component of a signal inside of the flexible cable 11 being difficult to drain to a ground. This prompts a high-frequency component to radiate from the flexible cable 11.